This invention relates to the field of replicated optics. In particular, the invention teaches how hard amorphous carbon coatings can be used to facilitate manufacture of replicated optical products in addition to providing products of superior durability.
Replicated optics are a known field of art. Various aspects and approaches to the field are described in U.S. Pat. Nos. 2,464,736 to White et al; 3,873,191 to Veret et al; 4,255,364 to Talbert and 4,453,587 to Gowan.
In general, a master optical article is provided to very close optical thickness, often to a surface smoothness of 1/4-wavelength of light. This master, usually formed of glass or other dimensionally-stable material, is coated with a release-facilitating layer (usually called merely a "release layer") then, usually, with a protective layer and, finally, a vacuum-deposited mirror-like, finish layer. The idea is to prepare a master from which one can transfer the reflective layer with the master's surface quality to a wholly different substrate article, thereby forming a replicated optical article. The surface of the substrate is often within about 0.0002-inch root mean square of the surface smoothness of the master.
This transfer is usually carried out by use of an adhesive based on organic resins such as epoxy or polyester resins. The adhesive, after appropriate mixing and deaereating, is poured onto the master or the substrate. Then the master is mated to the substrate with the excess resin being squeezed out around the periphery of the mated articles. When the resin is cured, the master can be separated away from the rest of the assembly at the release layer. The substrate now carries the reflective surface and is then defined as the "replicated optical" article. The replicated article is sometimes itself used as a "submaster" to create still another replicated optical article.
This process has been commercially successful, but as demand grows for improved products and higher yields of products, it has been desirable to seek new and improved ways to improve the process.
Other art, heretofore unrelated, to the art of optical replication, is that describing the formation of thin carbon coatings as infra-red reflective wear layers. See United Kingdom Pat. No. 1,582,231. Other publications relating to carbon coatings include U.S. Pat. No. 4,383,728 to Litington describing infra-red reflective surfaces, an article by Enke in Applied Optics/Volume 24, No. 4 of Feb. 15, 1985, and an article by Moravec and Lee in the Journal of Vacuum Sci. Technology of March 1982 following the terminology of Moravec and Lee, these carbons are known in the art as i-carbons.
The above assembly of prior art was necessarily made with full knowledge of the invention to be described below. It is emphasized that nowhere in the prior art was the technology of carbon coatings related to achieving any specific advantage in the field of replicated optics.